Ultrahigh thermal stability of carbon encapsulated Cu nanograin on a carbon nanotube scaffold

Nanograined (NG) materials have exhibited marvelous mechanical, physical and chemical properties due to their grain size effect. However, NG materials usually suffer from poor thermal stability even at ambient temperature, which severely limits their performance and practical applications. Here, we report a bottom-up assembly strategy of freestanding flexible hybrid composed of Cu nanograins attached on a carbon nanotube (CNT) scaffold. These Cu nanograins coated with a carbonaceous layer well maintain their stability even at ∼0.79 times of the melting temperature of coarse-grained Cu. Such a substantially enhanced thermal stability originates from the carbonaceous coating layer that effectively inhibits Cu atom diffusion and suppresses the morphology change of nanograins by applying a compressive hoop stress. The total volume fraction of the interface and grain boundary (GB) achieves a high value of ∼25.4%, much larger than that of conventional NG materials with comparable grain size. This hybrid possesses a good flexibility and scalability, which can be facilely tailored into any dimensions and shapes, thus availing to be transferred and integrated onto arbitrary substrate in various applications. Our approach is generally applicable to various of NG-CNT hybrids, shedding light on the design and fabrication of highly stable nanostructured materials.